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mastero 9th October 2006 09:49 AM

Need idea / help building a 5.1 surround system Amp.
Hello friends,

I have searched and could not find a perfect solution to my requirements.

As mentioned above i want to build a 5.1 system i have the following chips at my disposal.

LM4780 - 5 NOS
LM4781 - 5 NOS
LM3875 - 5 NOS

I want to have 2 front 2 rear 1 center and 1 woofer.


The inputs shall be from a 5.1 system so i can build a simple 6 channel amp and it will work great.

But i aslo want the have the Tv connected to it so that means the input shall be only two channels. This is where i am lost, the peramp section shall have to split it and make the 6channels.

I have checked the sound.west designs and found a 3.1 channel spiltter but i require 5.1 any idea shall be good.

Also what your experience suggest which chip shall be good to use for which channel. the list of the chip is above. I dont wann build a Transistor based Amp.

BTW : i have build a Car Amp (SA1216 based using this forums knowledge.)

Any idea / help shall be good.


pinkmouse 9th October 2006 10:06 AM

I would just feed the TV to left and right and sub, ( but you will need a crossover for sub use). Stereo TV is encoded in Dolby Prologic, which needs a decoder to send info to center and surround channels, but there are various analogue surround decoder circuits around that do a similar thing.

mastero 9th October 2006 10:19 AM

analogue surround decoder circuits

:) :) This is exactly what i want please show me a direction to look at if you know one .


pinkmouse 9th October 2006 10:50 AM

Rod Elliot helps out as always! :)

Nordic 9th October 2006 11:38 AM

Yep, you can search for more info on that project here too, I did play with it for a little while, and put it on the backburner for later optimisation, but it works...

mastero 10th October 2006 10:12 PM

Hello friends

I have decided on using 2 x 4780 (For front and rear channel) 1 x 3875 (For Center channel) and 1 x 4780 Parallel mode (For The Sub)

I have found numerous data for 4780 placement, Pcb and etc .. made a pcb on Express ...

Please let me know if i have missed something or if there is some errors.



mastero 11th October 2006 07:02 AM

Come on guys !

no one ?


mastero 12th October 2006 01:45 PM

Is there a "HELP ME" Button on this forum ?

Neway i have completed the preamp section but cant figure out how to add volume control to it.


Its in express pcb format.

CAN someone please tell me how to add volume control?

Will not supplying power (+ and -) to the TL082 work ?


mastero 13th October 2006 10:07 PM

:D Just completed the 5.1 Channel Amplifier.


4780 x 2 for front and rear speaker (60 W x 4)

4780 x 1 for Sub (120w)

3875 x 1 for Center (56W)

added a preamp with surround decoder so i can connect the DVD using its onboard decoder or TV and using the preamps onboard decoder.

Has three bipolar relay to swith six connections to DVD or TV.


Remote control

Temp sensors

Two digit Led display (Showing Temp and mode selected)

Auto start fan when temp is high.

and lets see. what comes to my mind.


rehanabid 14th October 2006 08:49 AM

First the link to your PCB doesnt work, probably thats why no one replied. Secondly I guess most of the DIYers use either Eagle or Protel. ExpressPCB may be a few.
If you want you files to be viewed and DIYers to give comments it would be nice if you post them here as PDF or JPG/PNG/BMP files.

Specs that you mentioned are fine, what need to be seen is, is there some area where DIYers could add value by suggesting improvements.
Volume control could be added easily at the input stage of the chips after adding some seperation in the form of OPAMP or cicuitary to prevent the previous audio section HDTV/etc from getting shorted.

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